1. Field of the Invention
The present invention relates to a magnetic head for perpendicular magnetic recording that is used for writing data on a recording medium by means of a perpendicular magnetic recording system, and to a method of manufacturing such a magnetic head.
2. Description of the Related Art
The recording systems of magnetic read/write devices include a longitudinal magnetic recording system wherein signals are magnetized in a direction along the plane of the recording medium (the longitudinal direction) and a perpendicular magnetic recording system wherein signals are magnetized in a direction perpendicular to the plane of the recording medium. It is known that the perpendicular magnetic recording system is harder to be affected by thermal fluctuation of the recording medium and capable of implementing higher linear recording density, compared with the longitudinal magnetic recording system.
Typically, magnetic heads for perpendicular magnetic recording have a structure in which a reproducing (read) head having a magnetoresistive element (that may be hereinafter referred to as an MR element) for reading and a recording (write) head having an induction-type electromagnetic transducer for writing are stacked on a substrate, like magnetic heads for longitudinal magnetic recording. The write head includes a pole layer that produces a magnetic field in the direction perpendicular to the plane of the recording medium.
For the perpendicular magnetic recording system, it is an improvement of the recording medium and an improvement of the write head that mainly contributes to an improvement in recording density. It is a reduction in track width and an improvement in write characteristics that is particularly required for the write head to achieve higher recording density. On the other hand, if the track width is reduced, the write characteristics, such as an overwrite property that is a parameter indicating an overwriting capability, suffer degradation. Better write characteristics are therefore required as the track width becomes smaller.
A magnetic head for use in a magnetic disk drive such as a hard disk drive is typically provided in a slider. The slider has a medium facing surface that faces toward the recording medium. The medium facing surface has an air-inflow-side end and an air-outflow-side end. The slider is configured to slightly fly over the surface of the recording medium by means of an airflow that comes from the air-inflow-side end into the space between the medium facing surface and the recording medium. The magnetic head is typically disposed near the air-outflow-side end of the medium facing surface of the slider. In a magnetic disk drive, the magnetic head is aligned through the use of a rotary actuator, for example. In this case, the magnetic head moves over the recording medium along a circular orbit about the center of rotation of the rotary actuator. In such a magnetic disk drive, a tilt of the magnetic head with respect to the tangent of the circular track, which is called a skew, occurs in accordance with the position of the magnetic head across the tracks.
In a magnetic disk drive of the perpendicular magnetic recording system, in particular, which exhibits a better capability of writing on a recording medium compared with the longitudinal magnetic recording system, if the above-mentioned skew occurs, there arise problems such as a phenomenon in which, when data is written on a certain track, data stored on a track adjacent thereto is erased (this is hereinafter called adjacent track erasing), or unwanted writing between two adjacent tracks. To achieve higher recording density, it is required to suppress adjacent track erasing. Unwanted writing between two adjacent tracks affects detection of servo signals for alignment of the magnetic head and the signal-to-noise ratio of read signals.
For preventing the problems resulting from the skew described above, there is known a technique in which an end face of the pole layer located in the medium facing surface is formed into such a shape that one of its sides located backward along the direction of travel of the recording medium (that is, the side located closer to the air inflow end of the slider) is shorter than the opposite side, as disclosed in U.S. Pat. No. 6,504,675 B1, for example.
As a magnetic head for perpendicular magnetic recording, there is known a magnetic head including the pole layer and a shield, as disclosed in U.S. Pat. No. 4,656,546, for example. In this magnetic head, an end face of the shield is located in the medium facing surface at a position forward of the end face of the pole layer along the direction of travel of the recording medium with a predetermined small distance provided therebetween. Such a magnetic head will be hereinafter called a shield-type head. In shield-type heads, the shield has a function of preventing a magnetic flux from reaching the recording medium, the flux being generated from the end face of the pole layer and expanding in directions except the direction perpendicular to the plane of the recording medium. The shield also has a function of returning a magnetic flux that has been generated from the end face of the pole layer and has magnetized the recording medium. Shield-type heads allow a further improvement in linear recording density.
U.S. Pat. No. 4,672,493 discloses a magnetic head having a central magnetic layer that serves as the pole layer and other magnetic layers that are respectively disposed forward and backward of the central magnetic layer along the direction of travel of the recording medium, with coils provided between the central magnetic layer and the magnetic layer disposed forward and between the central magnetic layer and the magnetic layer disposed backward, respectively. This magnetic head is capable of increasing components of the magnetic field generated from the medium-facing-surface-side end of the central magnetic layer, the components lying in the direction perpendicular to the plane of the recording medium.
Reference is now made to FIG. 18 to describe a basic configuration of shield-type heads. FIG. 18 is a cross-sectional view of a main part of an example of shield-type heads. This shield-type head includes: a medium facing surface 100 that faces toward a recording medium; a coil 101 for generating a magnetic field corresponding to data to be written on the recording medium; a pole layer 102 having an end located in the medium facing surface 100, the pole layer 102 allowing a magnetic flux corresponding to the magnetic field generated by the coil 101 to pass and generating a write magnetic field for writing the data on the recording medium by means of the perpendicular magnetic recording system; a shield layer 103 having an end located in the medium facing surface 100, the shield layer 103 being coupled to a portion of the pole layer 102 away from the medium facing surface 100; a gap layer 104 provided between the pole layer 102 and the shield layer 103; and an insulating layer 105 covering the coil 101. An insulating layer 106 is disposed around the pole layer 102. The shield layer 103 is covered with a protection layer 107.
In the medium facing surface 100, the end of the shield layer 103 is located forward of the end of the pole layer 102 along the direction T of travel of the recording medium, with a predetermined distance therebetween provided by the thickness of the gap layer 104. At least part of the coil 101 is disposed between the pole layer 102 and the shield layer 103 and insulated from the pole layer 102 and the shield layer 103.
The coil 101 is made of a conductive material such as copper. The pole layer 102 and the shield layer 103 are made of a magnetic material. The gap layer 104 is made of an insulating material such as alumina (Al2O3). The insulating layer 105 is made of photoresist, for example.
In the head of FIG. 18, the gap layer 104 is disposed on the pole layer 102 and the coil 101 is disposed on the gap layer 104. The coil 101 is covered with the insulating layer 105. One of the ends of the insulating layer 105 closer to the medium facing surface 100 is located at a distance from the medium facing surface 100. In the region from the medium facing surface 100 to the end of the insulating layer 105 closer to the medium facing surface 100, the shield layer 103 is opposed to the pole layer 102 with the gap layer 104 disposed in between. The length (height) of the portion where the pole layer 102 and the shield layer 103 are opposed to each other with the gap layer 104 disposed in between, as taken from the end closer to the medium facing surface 100 to the opposite end, is called throat height TH. The throat height TH has an influence on the intensity and distribution of the magnetic field generated from the pole layer 102 in the medium facing surface 100.
In a shield-type head, such as the one illustrated in FIG. 18, it is desirable to reduce the throat height TH to improve the overwrite property. It is required that the throat height TH be 0.1 to 0.3 μm, for example. When such a small throat height TH is required, the head of FIG. 18 encounters a problem that, during operation of the head, the insulating layer 105 expands due to heat generated by the coil 101 and consequently an end portion of the shield layer 103 closer to the medium facing surface 100 protrudes. The protrusion of the end portion of the shield layer 103 during operation of the head increases the possibility of collision of the slider with the recording medium.
U.S. Patent Application Publication No. US 2007-0121248 A1 and U.S. Patent Application Publication No. US 2007-0211377 A1 each disclose a magnetic head capable of solving the problem mentioned above. The magnetic head disclosed in each of these publications includes a shield having a first layer and a second layer. The first layer has an end face located in the medium facing surface. The second layer is disposed between at least part of the coil and the medium facing surface, and is magnetically connected to the first layer. In addition, the second layer has an end face closer to the medium facing surface, and this end face is located at a distance from the medium facing surface. The shield having such a structure will be hereinafter called a recessed shield.
The magnetic head employing the recessed shield is capable of suppressing the protrusion of the end portion of the shield closer to the medium facing surface induced by the heat generated by the coil. However, a problem was found to occur in the magnetic head employing the recessed shield, as described below. In the head employing the recessed shield, a nonmagnetic layer is provided between the medium facing surface and the end face of the second layer of the shield. The nonmagnetic layer is formed by sputtering, for example, using an inorganic insulating material such as alumina (Al2O3). In this case, it is difficult to achieve complete coverage by the inorganic insulating material over the end face of the second layer, and consequently a crack is likely to develop from the interface between the nonmagnetic layer and the end face of the second layer. The crack easily reaches the medium facing surface because the distance between the end face of the second layer and the medium facing surface is small. The crack impairs the reliability of the magnetic head.